Thursday, October 6, 2011

New paper finds relative sea-level rise in Greenland stabilized over past 400 years

A paper published today in Earth and Planetary Science Letters examines relative sea-level change over the past 700 years at three sites in Greenland. The paper finds relative sea-levels rose most rapidly between the 14th to 17th/18th centuries during the Little Ice Age, then slowed and were stable "during at least the latter part of the 20th century."

Abstract: This paper presents new evidence regarding relative sea-level (RSL) changes and vertical land motions at three sites in Greenland since 1300 A.D., a time interval that spans the later part of the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). We observe RSL rise at two sites in central west Greenland from c. − 0.80 ± 0.20 m at c. 1300 A.D. to c. − 0.20 m ± 0.25 m at c. 1600 A.D., after which RSL slowed and then stabilised. At a third site in south Greenland, we observe RSL rise from c. − 1.40 ± 0.20 m at c. 1400 A.D. until c. 1750 A.D., after which RSL slowed and was stable during at least the latter part of the 20th century. The c. 1600 A.D. RSL slow-down seen at the two former sites is surprising because it occurs during the LIA when one might expect the ice sheet to be gaining mass and causing RSL to rise. We interpret this RSL slowdown to indicate a period of enhanced regional mass loss from central west Greenland since c. 1600 A.D. and propose two hypotheses for this loss: first, a reduction in precipitation during cold and dry conditions and second, higher air temperatures and increased peripheral surface melt of the ice sheet from this date onwards. The latter hypothesis is compatible with a well-established temperature seesaw between western Greenland and northern Europe and, potentially, a previously identified shift from a positive to generally more negative NAO conditions around 1400 to 1600 A.D. Our study shows how RSL data from Greenland can provide constraints on the timing of ice sheet fluctuations in the last millennium and challenges the notion that during cold periods in northern Europe the ice sheet in west Greenland gained mass.

Highlights
► In the late Holocene, relative sea-level rise in west Greenland slowed at 1600 A.D. ► This is during the Little Ice Age and is unexpected. ► This records mass loss either due to less precipitation or warmer air temperatures. ► We favour warmer air temperatures, as are expected under negative NAO. ► Parts of the Greenland Ice Sheet can lose mass when it is cold elsewhere.